1. Field of the Invention
This invention relates to the art of continuously manufacturing an elongated cast product, for example, of copper and its alloy for use in electronic components.
2. Prior Art
With the development of the electronic industry, a copper alloy for use as lead frames of IC (Integrated Circuit), LSI (Large Scale Integrated Circuit) and the like has recently been required to have a higher strength and a better electric conductivity. Copper alloys containing active metals such as zirconium (Zr), chromium (Cr) and titanium (Ti) can meet with this requirement. However, such a copper alloy product is usually cast in the atmosphere, so that part of the active metals are oxidized to form oxides which are contained in the resultant cast product as inclusions. In addition, when this cast product is subjected to rolling, stringers are caused to develop in the rolled product. Such a product can not be used for lead frames. To avoid this difficulty, starting materials of the above-mentioned copper alloy may be melted and cast into an ingot under vacuum, and then the ingot is rolled into a bar, a strip or the like. However, this procedure is quite expensive and therefore is not practical.
Also, in the electronic industry, there has been a demand for a wire of pure copper having a diameter of less than 50 .mu.m. When such a copper wire is produced with an ordinary casting method, it is susceptible to breakage. It is thought that this difficulty arises from the presence of the inclusions such as oxides in the cast copper. To avoid this, a vacuum melting is necessary, but this is expensive and therefore not practical.
Further, an ingot produced by an ordinary vacuum melting has a relatively large diameter and must subsequently be subjected to a hot processing such as a hot rolling to reduce it to a desired diameter or cross-section. During this hot processing the scales on the ingot are forced into the wire, and part of the iron content of the rolls is transferred to the rolled wire. This also causes the breakage of the wire.